1. Field of the Invention
The present invention relates to a method for producing alcohols by hydrogen reduction of esters or lactones.
2. Description of the Related Art
Methods for producing alcohols by reduction of esters or lactones are important in chemical synthesis. It is generally considered difficult to reduce an ester or lactone group by catalytic reduction, and methods of using a stoichiometric amount or more of a metal hydride compound such as lithium aluminum hydride have been used frequently. The method by the catalytic hydrogenation, however, is superior from the points of drastic reduction of waste, sustainable chemistry, and safety operation. Therefore, there has been a need for its development. For this reason, there have been many proposals concerning alcohol production by catalytic hydrogenation of esters or lactones, for example, using a homogeneous or heterogeneous catalyst. There are recently more reports on the homogeneous catalyst, because it gives more variety in designing the catalyst than the heterogeneous catalyst.
Methods of producing alcohols by hydrogenation of esters and lactones using a heterogenous catalyst were reported. Meanwhile, JP-A-2001-247499 (Patent Document 1), JP-A-2004-300131 (Patent Document 2), JP-A-2005-524704 (Patent Document 3), J. Chem. Soc. Chem. Commun., 1980, 783 (Non-patent Document 1), J. Mol. Catal. A, 2001, 166, 345-349 (Non-patent Document 2), Angew. Chem. Int. Ed., 2006, 45, 1113 (Non-patent Document 3) and others describe homogenous hydrogenations of esters using a ruthenium complex comprising a ruthenium compound and an organic phosphine compound. WO2006/106483 (Patent Document 4) and WO2006/106484 (Patent Document 5) describe hydrogenations using a ruthenium complex containing a ruthenium compound and a bidentate or tetradentate aminophosphine ligand. Further, JP-A-2004-238306 (Patent Document 6) discloses a homogeneous carbonyl group-hydrogenating method using a ruthenium hydride catalyst.
However, the methods using heterogeneous catalyst demand a severe reaction condition at high temperature and/or high pressure, and thus, have significant limitation on operation, production apparatus and others. In addition, the hydrogenations described in Patent Documents 1 to 3 and Non-patent Documents 1 to 3 are not satisfactory both in yield and catalytic efficiency, and thus, may not be considered to be economically advantageous methods. Alternatively, a fluorine-containing alcohol is used as a solvent in the hydrogenations of ester described in Patent Document 2 and Non-patent Document 1, causing a concern about cost-effectiveness and environment load. Yet alternatively, the method described in Non-patent Document 2, which demands a high temperature of 180 to 200° C., causes a concern about cost-effectiveness and convenience of operation from the industrial viewpoint. Further, 1,4-dioxane, an economically disadvantageous and possibly harmful solvent, is used in the method disclosed in Non-patent Document 3. A ruthenium complex having a ligand containing both phosphorus and nitrogen atoms in the same molecule is used in the methods described in Patent Documents 4 and 5, and thus, it would be more complicated and difficult to prepare the ligand. Hydrogenation of an ester group is considered difficult in the method described in Patent Document 6 (see Example 8).